Nutrient Recovery Technologies Research Articles

Intensive Microalgal Cultivation and Tertiary Phosphorus Recovery from Wastewaters via the EcoRecover Process.

Mixed community microalgal wastewater treatment technologies have the potential to advance the limits of technology for biological nutrient recovery while producing a renewable carbon feedstock, but a deeper understanding of their performance is required for system optimization and control. In this study, we characterized the performance of a 568 m3·day-1 Clearas EcoRecover system for tertiary phosphorus removal (and recovery as biomass) at an operating water resource recovery facility (WRRF). The process consists of a (dark) mix tank, photobioreactors (PBRs), and a membrane tank with ultrafiltration membranes for the separation of hydraulic and solids residence times. Through continuous online monitoring, long-term on-site monitoring, and on-site batch experiments, we demonstrate (i) the importance of carbohydrate storage in PBRs to support phosphorus uptake under dark conditions in the mix tank and (ii) the potential for polyphosphate accumulation in the mixed algal communities. Over a 3-month winter period with limited outside influences (e.g., no major upstream process changes), the effluent total phosphorus (TP) concentration was 0.03 ± 0.03 mg-P·L-1 (0.01 ± 0.02 mg-P·L-1 orthophosphate). Core microbial community taxa included Chlorella spp., Scenedesmus spp., and Monoraphidium spp., and key indicators of stable performance included near-neutral pH, sufficient alkalinity, and a diel rhythm in dissolved oxygen.

Bioponic systems with biochar: Insights into nutrient recovery, heavy metal reduction, and microbial interactions in digestate-based bioponics

Bioponics is a nutrient-recovery technology that transforms nutrient-rich organic waste into plant biomass/bioproducts. Integrating biochar with digestate from anaerobic wastewater treatment process can improve resource recovery while mitigating heavy metal contamination. The overarching goal of this study was to investigate the application of biochar in digestate-based bioponics, focusing on its efficacy in nutrient recovery and heavy metal removal, while also exploring the microbial community dynamics. In this study, biochar was applied at 50 % w/w with 500 g dry weight of digestate during two 28-day crop cycles (uncontrolled pH and pH 5.5) using white stem pak choi (Brassica rapa var. chinensis) as a model crop. The results showed that the digestate provided sufficient phosphorus and nitrogen, supporting plant growth. Biochar amendment improved plant yield and phosphate solubilization and reduced nitrogen loss, especially at the pH 5.5. Furthermore, biochar reduced the heavy metal accumulation in plants, while concentrating these metals in the residual sludge. However, owing to potential non-carcinogenic and carcinogenic health risks, it is still not recommended to directly consume plants cultivated in digestate-based bioponic systems. Additionally, biochar amendment exhibited pronounced impact on the microbial community, promoting microbes responsible for nutrient solubilization and cycling (e.g., Tetrasphaera, Herpetosiphon, Hyphomicrobium, and Pseudorhodoplanes) and heavy metal stabilization (e.g., Leptolinea, Fonticella, Romboutsia, and Desulfurispora) in both the residual sludge and plants. Overall, the addition of biochar enhanced the microbial community and facilitated the metal stabilization and the cycling of nutrients within both residual sludge and root systems, thereby improving the overall efficiency of the bioponics.

Combination of technologies for nutrient recovery from wastewater: A review

The growing human population is increasing the need for crop production, which has resulted in elevated requirements of Nitrogen-Phosphorous-Potassium (NPK) fertilisers. This tremendous demand cannot be sustained on traditional processes, which cause significant resource depletion and unacceptable environmental impacts due to their heavy reliance on fossil fuels. To overcome this, alternative sources to obtain fertilisers have been explored, including the recovery of nutrients from wastewater and waste streams. However, this approach faces several challenges, such as the dilution of the streams, low public acceptance, and lack of support. With the aim of surpassing these barriers, the present study provides a review of existing Research & Development (R&D) projects in the field, comparing the available technologies to identify the optimal train of technologies for nutrient recovery: Anaerobic Digestion followed by the valorisation of the digestate (directly or producing P-based fertilisers such as P salts, CaP, H3PO4 and P2O5) and the liquid fraction (obtaining struvite, ammonium sulphate/nitrate, and reclaimed water). Moreover, an innovative strategy for nutrient recovery based on the decentralised treatment of separated concentrated streams is proposed as a useful strategy for valorising nutrients, developing a Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis. Finally, non-technological strategies are suggested to mainstream waste valorisation, aimed at overcoming social barriers by promoting stakeholder acceptance and producing recycled fertilisers with low associated rejection. Nutrient valorisation through the decentralised treatment of source separated waste/wastewater using optimised train of technologies seems a sustainable strategy for addressing the current and future massive demand of fertilisers.

Improving BioWin Modeling of Phosphorus Solubilization in Acid-Phase Digesters

BioWin 6.0 does not accurately predict phosphorus (P) speciation in acidogenic anaerobic digesters under default kinetics characterization and parameterization. The accurate modeling of acid-phase digestion is needed to predict the performance of novel nutrient recovery technologies that act on these digester effluents. The main thrust of this work was to identify and correct the causes of inaccurate P partitioning and precipitation within BioWin models of acid-phase digestion reactors. A BioWin configuration including an organic acid digester was parameterized and recalibrated based on the known traits of acid-phase digestion and then validated against a full-scale digester in a municipal wastewater treatment plant. This digester, with pH 5.14 and 61–74% solubilized P, was predicted by BioWin default parameters to have only 27% soluble P and a net formation of P precipitates. Corrections to the polyphosphate-accumulating organism decay, endogenous product decay, hydrolysis rate, and brushite behavior resulted in 67% solubilization with no precipitate formation. Cabinet configurations showed similar behavior when modified to include an acid-phase digester under default parameters, but predictions were similarly amended by our parameter changes. This improved modeling technique should allow operators to effectively characterize acid digesters for their own treatment trains and allow engineers to predict the performance of novel nutrient recovery technologies acting on acidogenic digest.

Eco-friendly and sustainability assessment of technologies for nutrient recovery from human urine—a review

Nitrogen (N), phosphorus (P), and potassium (K) represent the primary components of commercial NPK fertilizer and are primarily derived from finite resources through complex and expensive processes. To ensure global food security, the development of sustainable and eco-friendly procedures for fertilizer production has gained attention. Humans generally excrete urine containing 11 g of N/L, 0.3 g of P/L of P and 1.5 g of K/L, which benefit plant growth. The recovery of these essential plant nutrients from human urine has become the focal point of increasing research endeavors. Despite the potential advantages of nutrient recovery from urine, this process is complicated, and the economic implications are substantial. Furthermore, human urine may harbor undesirable contaminants, such as pathogens, pharmaceutical residues, hormones, and elevated salt levels, which could be disseminated into the environment through agriculture. This study appraised various emerging technologies for nutrient recovery from human urine, considering their challenges, environmental impact, economic viability, and the overall sustainability of the processes. This review elucidated that most nutrient recovery technologies demonstrated elevated efficiency in nutrient recovery. Nevertheless, a recurrent oversight involves neglecting the potential transfer of contaminants and pathogens into environmental matrices. The complexity of these processes and their economic feasibility vary, with some proving intricate and economically unviable. Given that no singular technology fully mitigates these challenges, integrating two or more technologies appears imperative to address drawbacks and enhance overall system performance.

Electrochemical Phosphorous Recovery from Wastewater: Modeling & Scale-up Considerations

The prospect of electrifying the recovery of valuable nutrients from waste streams is of great interest in the effort of reducing the overall energy consumption and environmental impact of nutrient usage. Currently, many electrochemical precipitation technologies exist, and some have shown energy consumption values on par with implemented nutrient recovery technologies (both gravimetric for specified products and volumetric for waste stream handling). However, electrochemical precipitation technologies are at low-to-intermediate Technology Readiness Levels (TRLs) and need to be optimized and scaled to determine the feasibility of implementing them industrially. This presentation discusses necessary considerations for modeling and scaling electrochemical precipitation technologies from the perspective of phosphorus (P) recovery.Two specific modeling tools were used to study P recovery as struvite. Mass transport and electrochemical phenomenon were modeled using COMSOL within a stirred batch reactor format. The COMSOL modelling yields valuable information about limiting conditions, spatial distribution of dissolved species concentrations, and the effects of various reactor conditions (e.g., stirring or applied potential). Next, the precipitation of struvite under various solution conditions is discussed with respect to a thermodynamic model of precipitation developed using OLI Flowsheets. The precipitation study is then discussed with respect to modeled reactor conditions to ascertain information relevant to scaling electrochemical P precipitation. Figures of Merit (FOM) useful in scaling electrochemical reactions are highlighted to alleviate the dependence on the reactor design used for modelling, enabling a transfer of information to other reactor formats.

Sustainable resource recovery and process improvement in anaerobic digesters using hydrochar: A circular bio‐economic perspective

AbstractHydrothermal carbonization (HTC) is a promising technology for waste valorisation and nutrient recovery to achieve sustainability. HTC converts organic waste into hydrochar, a carbon‐rich solid with numerous surface functionalities that can be used for energy and wastewater treatment. In this review, we highlight the potential of hydrochar‐based technology for improving the performance of anaerobic digestion (AD) systems and downstream applications of nutrient‐laden hydrochar. We identify knowledge gaps in hydrochar production, performance in AD systems and nutrient recovery, including the need for larger‐scale production facilities, multielement adsorption studies, and computational modelling. Techno‐economic analysis and life cycle assessment of hydrochar applications are critical to evaluating the commercial viability of this technology. Overall, hydrochar‐based technology offers a sustainable solution for waste management and resource recovery, with potential socioeconomic benefits for developing economies. The deployment of hydrochar‐based technology will directly address key issues highlighted in the United Nations' Sustainable Development Goals such as Clean water and sanitation (SDG 6); Zero hunger (SDG 2); and Climate action (SDG 13) thereby contributing to a more sustainable future.

Tuna sidestream valorization: a circular blue bioeconomy approach.

Tuna is an economically significant seafood, harvested throughout the world, and is heavily traded due to its high nutritional quality and consumer acceptance. Tuna meat is rich in essential nutrients such as amino acids, polyunsaturated fatty acids (PUFA), and trace minerals. The huge volume of solid and liquid sidestreams generated during the processing stages of tuna is creating environmental and socioeconomic challenges in coastal areas. Different products such as fish meal, protein hydrolysates, collagen, enzymes, oil, and bone powder can be produced from tuna sidestreams. Using different nutrient recovery technologies like enzymatic hydrolysis, chemical processing, and green technologies, various categories of product value chains can be created in line with the conventional processing industry. This review attempts to provide a route map for the tuna industry for achieving the circular blue-bioeconomic objectives and reorient the irregular utilization pattern into a sustainable and inclusive path.

Modeling an acid-phase digester in BioWin with parameter optimization from site data

Organic acid digesters are reactors of growing interest for municipal nutrient recovery technologies, but the industry standard BioWin modeling software does not accurately predict their performance. A BioWin configuration using default parameters will over-predict volatile fatty acid production in an acid digester, yielding an unrealistically low pH. We have characterized the effects of parameters for local pH inhibition thresholds, growth and decay kinetics, and hydraulic residence times to successfully facilitate more accurate modeling of acid phase digestion reactors in BioWin. These changes show improvements in a range of treatment train models without affecting accuracy in other reactors. Results were calibrated against a municipal acid phase digester to accurately predict pH, VFA concentration, and gas production. In particular, an acid digester with a measured suspension pH of 5.14 was predicted by BioWin using default parameters to exist at pH 4.35 with highly sensitive biogas methane content, but our parameter changes were able to correct the predicted suspension pH and VFA concentrations over a range of values. We also demonstrate that several intuitive or traditional parameters a BioWin user may attempt, such as growth and fermentation kinetics, do not yield meaningful results. Refinements incorporated into BioWin should allow future operators to easily model acid digesters for their specific treatment trains or allow users to predict changes while testing new wastewater treatment technologies.

Preliminary Study on the Preparation of Conductive Nanosized Calcium Carbonate Utilizing Biogas Slurry by a Synchronous Double Decomposition Coating Method.

Nanosized calcium carbonate (NCC) plays a vital role in the rubber and plastic fields as a filler, but it cannot resolve the electrostatic problem. Humic-acid-based NCC (HA-NCC) was accidentally discovered in the reaction between biogas slurry and calcium chloride (CaCl2), based on nutrient recovery and gradient treatment technology to solve the biogas slurry problem. A preliminary study on the preparation of conductive nanosized calcium carbonate (CNCC) from the HA-NCC was implemented. Meanwhile, a synchronous double decomposition coating method was proposed to properly explain the formation of HA-NCC in the biogas slurry. The CNCC was further obtained through drying and carbonizing the HA-NCC sample. The morphology of CNCC was a square shape with aggregation, and its crystals were calcite. The C content of CNCC was 5% higher than that of the normal CaCO3, implying a synchronous coating effect of soluble HA in biogas slurry on NCC. The weight loss of CNCC was about 2.5% at 630 °C, explaining why the HA-NCC remained black at 550 °C for 4 h. The CNCC was partly ordered and graphitized. The resistivity of the CNCC reached 2.62 × 106 Ω·cm. It could be used as a conductive powder. In view of the favorable characteristics described above, CNCC would be expected to be a filler and antistatic agent for plastics and rubbers to enhance the tensile and bending resistance of polymer materials, while eliminating electrostatic hazards. The results are also of great significance for developing high-end products to realize resource utilization of biogas slurry.

Resource-Oriented Sanitation: On-Farm Septage Treatment and Nutrient Recycling for Sustainable Agriculture in the Philippines

Nutrient recovery technologies have been constantly developed and optimised to address challenges in water and wastewater management, sanitation, and agri-food systems, while promoting sustainable management of resources and circular phosphorous economy. However, these technologies have been rarely explored beyond the laboratory-scale in developing countries where it is mostly needed. In this study, a nutrient recovery batch reactor system was installed at a local farm in the Philippines to process raw septage from an onsite sanitation system, a septic tank, to recover a high-value fertiliser for local crop production. The batch reactor was used for two processes, namely acid hydrolysis for pre-treatment of septage and chemical precipitation for recovered phosphorous fertiliser (RPF). The recovered fertiliser was then applied to produce eggplants and tomatoes, which are the common crops grown in the farm. Results show that an average of 290 g of RPF was produced for every 100 L of raw septage processed. With hydrolysis, 77% of the phosphate concentration were released as phosphates from the solid component of the raw septage. About 98.5% of phosphates were recovered from the hydrolysed septage. The RPF when applied to the farm’s eggplants and tomatoes has yields comparable to that of the commercial fertilisers. This study was able to demonstrate the potential of a resource-oriented sanitation system that promotes nutrient recycling towards sustainable agriculture that further leads to meeting the United Nations sustainable development goals, particularly zero hunger (goal 2), clean water and sanitation (goal 6), sustainable cities and communities (goal 11), and responsible consumption and production (goal 12).

Incorporation of main line impact into life cycle assessment of nutrient recovery from reject water using novel membrane contactor technology

Wastewater treatment plant (WWTP) nutrient recovery has recently gained traction in the search for new pathways for fertilizer production. In particular, concentrated waste streams such as reject water from sludge digestion are suitable. The environmental impact of a novel nutrient recovery technology using a membrane contactor (NPHarvest) was examined with an environmental life cycle assessment (LCA). Impact hotspots were benchmarked against a comparable technology (struvite precipitation and ammonia stripping), and the impacts of the two technologies were found to be similar for most studied environmental impact categories. To allow for the inclusion of effects on other parts of the WWTP while limiting the general system boundaries to the reject water treatment, a novel approach to capture the main line impact was developed. The effects on the main line contributed substantially to the overall results. The overall results indicated clear nutrient recovery benefits related to substituted materials in mineral fertilizer production. Additionally, reject water nutrient recovery provided even greater benefits due to reduced N2O emissions and the reduced use of precipitation chemicals in the WWTP main line. Nonetheless, both nutrient removal and recovery were necessary for the two technologies to reach a net zero climate impact in their current pilot scales. Further development of the NPHarvest technology—such as mitigating NH3 emissions, exploring alternative input chemicals and optimizing energy consumption (especially for crystallizing the ammonium salt solution that is produced)—is recommended before full-scale implementation.

Nutrient recovery through struvite precipitation from anaerobically digested poultry wastewater in an air-lift electrolytic reactor: Process modeling and cost analysis

Anaerobic digested poultry wastewater (ADPW) is characterized by high levels of nutrients (nitrogen and phosphorus), which need to be removed and recovered before the wastewater is discharged into water bodies with advanced nutrient recovery technologies that are cheap and eco-friendly. In this study, an innovative air-lift electrolytic reactor (ALER) with a magnesium anode was developed for phosphate (PO43−) and ammonia–nitrogen (NH3–N) recovery from anaerobically digested poultry wastewater through electrochemical struvite (MgNH4PO4‧ 6H2O) precipitation. Under constant current density (12.4 A/m2) and superficial velocity (107.42 m/h), the maximum removal efficiencies of PO43− and NH3–N were 99.9% and 97.3%, respectively. Kinetic modeling revealed that PO43− and NH3–N removal from the liquid phase by the ALER followed a pseudo-first-order reaction model, with rate constants (k) of 0.0188 min−1 and 0.0143 min−1, respectively. The recovered precipitate was characterized with FTIR, XRD, and SEM-EDS which also identified that precipitates as high-purity (88.5%) struvite with a mean particle size of 142.95 μm. Mean particle size and size distribution were found to be linearly increased with superficial upflow velocity. The electrical energy consumption per order (EEO) of the ALER was 0.824 kWh/m3, and the space–time yield is achieved at 0.988 kg/m3h with a corresponding operating cost of 3.87 $/m3. The ALER process has proven to be energy efficient in nutrient recovery from ADPW with struvite products suitable to be used in agricultural practices.

Energy Demand of Nitrogen and Phosphorus Based Fertilizers and Approaches to Circularity

The climate-related concerns associated with the manufacturing of synthetic fertilizers are largely traced back to energy and carbon emissions during the chemical manufacturing of ammonia. However, synthetic fertilizers are made up of several macronutrients (nitrogen, phosphorus and potassium), each with different energy intensities and environmental impacts. With the movement toward resource circularity, there is a need to create a more holistic view regarding the process energy associated with synthetic inorganic fertilizers, including nitrogen and phosphorus. Here, we first describe the growing production and consumption of inorganic (synthetic) and organic (animal waste) nutrients in agriculture as well as the process energy associated with the production of granular phosphorus and nitrogen-based fertilizers. Next, we present projected global demand of nitrogen and phosphorus nutrients based on various sustainability and societal equity scenarios to make an argument for nutrient recovery as a viable approach to meet this demand. Finally, we discuss the characteristics and challenges of emerging technologies for nutrient recovery along with baseline performance and costs of current operational recovery facilities.

Nutrient recovery technologies for management of blackwater: A review

Nutrient recovery and recycling are of great importance in sustainable development. Blackwater (BW) refers to wastewater from toilets, which contains feces, urine, water, and toilet paper from flush toilets. The highly concentrated nutrients of blackwater could be collected through source separation and treated adequately to recover nutrients efficiently and economically. The review intends to give an overview of the characteristics of BW and different techniques to recover nutrients and other valuable products. A number of these technologies are currently under development or being tested at laboratory or pilot scale. The perspective for blackwater nutrient recovery technologies is very positive due to their great potential. For application of source-oriented sanitation infrastructure and systems, there is still a long way to go for development of commercial technologies and valuable products.

Carbon footprint of dairy manure management chains in response to nutrient recovery by aerobic pre-treatment

Aerobic pre-treatment of liquid dairy manure has previously been reported as an effective nutrient export and emissions mitigation approach. The first objective of this study was to experimentally determine the optimal intermittent aeration ratio for nutrient recovery from liquid dairy manure through an on-site pilot-scale reactor to partially reduce the required energy for the aerobic process. The second objective was to theoretically investigate the total carbon footprints of direct manure spreading on croplands and permanent manure storage in open anaerobic lagoons in response to nutrient removal by the optimal determined intermittent aerobic treatment ratio. Four scenarios (S) were included; S1 was the traditional scenario of manure spread on croplands without the aerobic pre-treatment, S2 was the modified scenario of manure spread on croplands that included the aerobic pre-treatment, S3 was the traditional scenario of manure storage in lagoons, and S4 was the modified scenario of manure storage in lagoons that included the aerobic pre-treatment. The results showed that comparable nutrient removal efficiencies could be obtained with a 5:1 intermittent aeration ratio. Total nitrogen (TN) and total phosphorus (TP) were recovered were 41.5 ± 1.3% and 37.0 ± 4.0%, respectively, in ammonium sulfate and phosphorus-rich sludge, while 55.3 ± 1.4% of the chemical oxygen demand (COD) was removed. The estimated total carbon footprint for S1, S2, S3, and S4 were 24.4, 37.9, 45.3, and 45.9 kg CO2-eqton−1, respectively. However, the total carbon footprint of S2′ and S4′, which used renewable-based energy to run the reactor instead of fossil-based energy used in S2 and S4, were estimated to 29.5 and 37.5 kg CO2-eqton−1, respectively. Clearly, applying the aerobic pre-treatment increased the total carbon footprint of all cases except S4′, in which the total carbon footprint was mitigated by −17.2%. Accordingly, the aerobic pre-treatment is only recommended in the case of S4’ from a carbon footprint point of view although it is an effective nutrient recovery technology.

Pathogens inactivation in nutrient recovery from urine: A review

Urine source separation, a kind of new sewage management concept, has made great progress in technology development and application in the past 30 years. However, understanding of the potential microbial risks in reuse of urine-derived fertilizer products (UDFPs) in agriculture is still lacking. Outbreak of pandemic of Coronavirus Disease 2019 and more deadly disease caused by Monkeypox strongly sounds the alarm bell to the attention on pathogens in urine and their fate in UDFPs. Therefore, this study presented a comprehensive review on pathogens inactivation in nutrient recovery technologies. The review suggests that technologies using alkaline or heating treatment can effectively reduce pathogens in UDFPs. However, technologies with characteristics such as membrane rejection of nutrients or nutrient adsorption may even concentrate pathogens in their fertilizer products. Based on an overall assessment, connections of technologies and the pathogens inactivation in their UDFPs have been established. This would help to provide a perspective on development of urine treatment technology and management of microbial risks in reusing urine nutrients in agriculture.

Review on the assessment model of nutrient recycling with agricultural residues treatment technologies

The technology for nutrient resource utilization of agricultural residues is crucial to realizing a circular agricultural economy. The assessment model provides essential support to optimize nutrient recovery and treatment technologies. We specifically summarized research progress in the assessment framework of agricultural residues nutrient recycling technology, assessment models and evaluation indicators, data sources of models and their uncertainty analysis, and the application scale of models. We found that process mathematical models and industrial eco-logy models are the common nutrient flow assessment models. Process mathematical and industrial ecology models differed greatly in terms of the reliability of assessment results and the simulation scale. The former mainly focused at laboratory or pilot scale, with higher accuracy. The latter could achieve multi-scale simulation from microscopic to macroscopic and had higher uncertainty, due to the way its data were obtained. Finally, we provided an outlook on the research on the assessment model of agricultural residues nutrient resource utilisation technology. In order to achieve accurate assessment of waste resource utilisation technology in agricultural production systems at the regional scale, a reliable model framework and database should be established by combining process mathematical models with industrial ecology models. Meanwhile, we should carry out research on model expansion at the geographical scales of factory scale, farm scale, village scale, township scale, and regional scale.

Environmental and Economic Impacts of Managing Nutrients in Digestate Derived from Sewage Sludge and High-Strength Organic Waste.

Increasingly stringent limits on nutrient discharges are motivating water resource recovery facilities (WRRFs) to consider the implementation of sidestream nutrient removal or recovery technologies. To further increase biogas production and reduce landfilled waste, WRRFs with excess anaerobic digestion capacity can accept other high-strength organic waste (HSOW) streams. The goal of this study was to characterize and evaluate the life-cycle global warming potential (GWP), eutrophication potential, and economic costs and benefits of sidestream nutrient management and biosolid management strategies following digestion of sewage sludge augmented by HSOW. Five sidestream nutrient management strategies were analyzed using environmental life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) for codigestion of municipal sewage sludge with and without HSOW. As expected, thermal stripping and ammonia stripping were characterized by a much lower eutrophication potential than no sidestream treatment; significantly higher fertilizer prices would be needed for this revenue stream to cover the capital and chemical costs. Composting all biosolids dramatically reduced the GWP relative to the baseline biosolid option but had slightly higher eutrophication potential. These complex environmental and economic tradeoffs require utilities to consider their social, environmental, and economic values in addition to present or upcoming nutrient discharge limits prior to making decisions in sidestream and biosolids management.

Ligand-Enabled Donnan Dialysis for Phosphorus Recovery from Alum-Laden Waste Activated Sludge.

While many nutrient recovery technologies target liquid waste streams, new strategies are required for effective phosphorus recovery from solid waste. This study reports an innovative ligand-enabled Donnan dialysis process to recover orthophosphate (P(V)) from alum-laden waste activated sludge (WAS). Four ligands, namely acetate, citrate, ethylenediaminetetraacetate (EDTA), and oxalate, were evaluated for P(V) release from a synthetic sludge containing 5 mM P(V) and 25 mM Al(III) and a real, alum-laden WAS with similar contents. Citrate and EDTA released more than 95% of P(V) at doses of 30 mM, outperforming acetate and oxalate. The ligand-based solubilization strategy was coupled with Donnan dialysis to recover P(V) into a clean sodium chloride draw solution. After Donnan dialysis with the synthetic sludge, the P(V) recovery's order was as follows: EDTA (54.4%) > citrate (41.7%) > oxalate (4.3%). The P(V) recovery efficiencies were slightly lower for Donnan dialysis with real, alum-laden WAS, namely 45.1% and 25.2% for EDTA and citrate addition, respectively, due to competitive effects exerted by other dissolved species. These promising results successfully demonstrated the proof-of-concept for ligand-enabled Donnan dialysis.